DE69612074T2 - Brake control device for a motor vehicle - Google Patents

Description

This application is based on the prior Japanese Patent Application No. Hei.7-341456 filed on December 27, 1995, the priority of which is claimed and the contents of which are incorporated herein by reference.

Background of the invention 1. Field of the invention:

The present invention relates to a brake control device mounted on a motor vehicle.

2. Description of the state of the art

JP-A-7-89432 discloses a brake booster for a motor vehicle. In the brake booster, the brake pressure is boosted to a higher value during braking performed in a panic situation than in the normal situation in order to apply a higher brake pressure to the wheel cylinders. That is, by boosting the brake pedal stroke for the driver or the depression force with a higher assist ratio of a brake booster than in the normal operation, a higher brake pressure to be generated at the master cylinder is obtained.

In general, the reaction force of a brake pedal increases, and the load on the driver increases as the driver continues to press the brake pedal and resists this reaction force. Therefore, due to this load, it is difficult for the driver to or in a similar situation to further depress the brake pedal. Therefore, in the case of a conventional brake booster, due to the increase in the assist ratio of the brake booster, the burden on the driver caused by the reaction force of the brake pedal cannot be reduced, especially in a panic situation. Thus, when a female or elderly person depresses the brake pedal in the case of a conventional brake booster, despite the intention to obtain a higher braking force, it is difficult to obtain the higher braking force.

Furthermore, when the driver depresses the brake pedal to stop the vehicle at the target point, he can only depress the brake pedal strongly during the initial braking when the reaction force of the brake pedal is not yet felt. However, when the reaction force received by the brake pedal becomes large due to the strong depression, the driver is likely to release the brake pedal more or less contrary to his desire to stop the vehicle. This could occur in a braking situation where an almost emergency braking must be performed. In this case, the driver can only receive a braking force that is less than expected. Consequently, there is a tendency for the distance required to stop the vehicle with respect to its target point to be extended contrary to estimates.

Further information regarding the state of the art can be found in DE 43 25 940, which relates to a method for determining the start and end of an automatic braking process. If a setpoint is exceeded, the automatic braking process begins. To optimize the initiation of the automatic braking process, the threshold value is changed according to the driving condition. It is proposed to change the threshold value depending on of the vehicle speed at the time the brake pedal is depressed and independently of this depending on the position of the brake pedal. This document further describes different criteria for terminating the automatic braking process depending on the brake pedal application force, the vehicle speed and the pedal displacement.

DE 40 28 290 C1, referred to in the above document, discloses a method for shortening the braking distance in critical driving situations, wherein the exceeding of a first threshold value with regard to the driver's brake pedal actuation speed is the criterion for initiating an automatic braking process and wherein, directly after the start of the automatic braking process, a brake pressure pB,max is built up which corresponds to the brake pressure value with optimal deceleration of the vehicle.

Summary of the invention

In view of the above-mentioned problems, the present invention has an object to provide a brake control device for a vehicle which can generate a high braking force even if the operation amount of a brake operating member decreases to some extent.

To solve the above problems, the present invention provides a braking force increasing device, ie a brake control device for a vehicle, as defined in independent claim 1. Preferred embodiments of the invention are defined in the dependent claims. In this braking force increasing device, the braking force is continuously increased when a brake operating element is operated by a driver. and a change in the driver's operation of the brake operating member is within a predetermined range. For example, the brake pedal functions as a brake operating member when the driver operates a brake pedal to apply a braking force to the vehicle. The change in the driver's operation of the brake pedal can be detected based on an output signal from a brake pedal stroke sensor or a pressure sensor for detecting the braking pressure generated by a pressure generating device such as a master cylinder for generating a braking pressure in response to depression of the brake pedal.

Due to the brake force increasing device, the braking force can gradually increase even if, for example, the driver essentially keeps the depression of the brake pedal at a certain stroke. Therefore, it is not necessary for the driver to depress the brake pedal more strongly in order to cause braking force to be applied to the vehicle.

If a brake pedal stroke or the fact that the vehicle is braking is detected when the vehicle body is decelerating, the situations in which an emergency braking operation is carried out, braking in a panic situation is carried out and the vehicle is stopped at a target point can be judged. As a result, the state of the vehicle and the state of the driver in which an increase in the braking force is possible can be determined more appropriately.

Short description of the drawings

These and other objects, features and characteristics of the present invention will become apparent upon review of the following detailed description, the appended claims and the drawings, all of which form part of the application. In the drawings:

Fig. 1 is a schematic block view of a brake control device according to the invention for a motor vehicle,

Fig. 2 is a flow chart for explaining the content of arithmetic processing executed by an electronic control unit 50,

Fig. 3 is a diagram showing the function of the brake control device for a motor vehicle according to the present invention, and

Fig. 4 is a schematic block view of a brake control device for a motor vehicle according to the other embodiments.

Detailed description of the preferred embodiments

A first embodiment of a brake control device to which the present invention is applied will be explained based on the accompanying drawings.

Fig. 1 shows a schematic view of the first embodiment according to the present invention. In the first embodiment, the brake control device is applied to a front-wheel drive vehicle with an X-shaped piping system in which a front right wheel is connected to a rear left wheel and a front left wheel is connected to a rear right wheel.

In Fig. 1, when a driver depresses a brake pedal 1, a braking force is generated on a vehicle. The brake pedal 1 is connected to an amplifier 2. A depressing force applied to the brake pedal 1 and a pedal stroke thereof are transmitted to the amplifier 2. The brake pedal 1 turns on and off a brake switch 22 for activating a brake lamp in response to the depression thereof. The illumination of the brake lamp allows the driver of a following vehicle or similar vehicles to visually recognize that the vehicle is in a braking state due to the depression of the brake pedal 1. A stroke sensor 30 is provided on the brake pedal 1 to detect a moving distance of the brake pedal 1 when depressed by the driver.

The booster 2 has at least a first chamber and a second chamber. The first chamber is used as an atmospheric pressure chamber and the second as a vacuum chamber. A negative pressure generated in an intake manifold of an engine or by a vacuum pump is introduced into the vacuum chamber. The booster 2 directly amplifies the pedal depression force by the driver or the pedal stroke through a pressure differential between the atmospheric pressure chamber and the vacuum chamber. The booster 2 has a push rod for transmitting the amplified depression force or the pedal stroke to a master cylinder 3. The push rod pushes a master piston located in the master cylinder 3 so that a master cylinder pressure PU is generated. Here, the master cylinder is provided with a master reservoir 3a exclusively for supplying the brake fluid to the master cylinder 3 or for storing excess brake fluid in the master cylinder.

As described above, a vehicle is usually provided with a brake fluid pressure generating device consisting of a brake pedal 1, a booster 2, a master cylinder 3 and the like for generating braking force on the vehicle.

A first line A extending from the master cylinder 3 branches off in the middle. A first wheel cylinder 4 for providing braking force to a front right wheel FR and a second wheel cylinder 5 for providing braking force to a rear left wheel RL are connected to both ends of the first branch line A. A control valve 101 is provided in the line extending from the master cylinder 3 to the branch point of the first line A. That is, the control valve 101 divides the first line A into two parts: a first line section A1 extending from the master cylinder 3 to the control valve 101 and a second line section A2 extending from the control valve 101 to the respective wheel cylinders 4 and 5.

A braking force generating device for generating a braking force on the vehicle has a brake pedal 1, a master cylinder 3, first and second line sections A1 and A2, and first and second wheel cylinders 4 and 5.

An outlet port of a pump 102, which receives the brake fluid from the main accumulator 3a provided exclusively with the master cylinder 3, is connected to the second line section A2. Here, a check valve is provided with an outlet line B for connecting the outlet port of the pump 102 and the second line section A2 and with an inlet line C for connecting an inlet port of the pump and the main accumulator 3a. The check valves prevent the brake fluid from flowing in the opposite direction from the pump 102 to the main accumulator 3a and from the second line section A2 via the pump 102.

Wheel cylinder pressure sensors 31 and 32 are provided with a first and a second wheel cylinder 4 and 5, respectively, so that the brake fluid pressure applied to each wheel cylinder can be detected. Here, the wheel cylinder pressure sensors 31 and 32 are not necessarily provided on first and second wheel cylinders 4 and 5, but may be provided at points in the second line section A2 at which equivalent brake fluid pressures can be detected, such as in the corresponding wheel cylinders 4 and 5.

Thus, wheel speed sensors 20 and 21 such as electromagnetic transducer type wheel speed sensors are provided at the front right wheel FR and the rear left wheel RL. Wheel speed signals detected by the wheel speed sensors 20 and 21, output signals from each of the wheel cylinder pressure sensors 31 and 32, an output signal from the stroke sensor 30 and an output signal from the brake switch 22 are supplied to an electronic control unit (ECU) 50 described later for performing calculations as shown in Fig. 2.

The electronic control unit 50 is composed of a microcomputer having a CPU, a ROM, a RAM, an input/output interface, etc. In addition, the electronic control unit 50 processes wheel speed signals detected by wheel speed sensors 20 and 21 as described above and control operations of the control valve 101 and the pump 102 by supplying control signals thereto.

In the brake control device of the first embodiment, an increasing means 100 for increasing the braking force by increasing the wheel cylinder pressures acting on the wheel cylinders 4 and 5 under predetermined conditions includes the control valve 101 and the pump 102, and is controlled by the electronic control unit 50.

In the first embodiment, a 2/2-way valve is used as control valve 101 to connect the connections by moving its valve body upon energization of the coil therein when electric current is supplied to the coil based on signals from the electronic control unit 50. The position of the control valve 101 shown in Fig. 1 indicates a state in which the terminals of the control valve 101 are interrupted when electric current is supplied based on the control signal from the electronic control unit 50. The terminals thereof are connected in the normal braking mode in which no electric current is supplied.

In the above description, only the structure of the first pipe A was explained. However, since the same structure can be used in the second pipe connecting a front left wheel cylinder to a rear right wheel cylinder, a detailed explanation will not be made.

Next, the content in the arithmetic processing of the electronic control unit 50 will be explained based on the flow chart in Fig. 2.

The flowchart in Fig. 2 starts with a driver turning on an ignition switch or a similar operation. Flags and calculated values used in the operational processing are initialized accordingly. First, each wheel speed VW is calculated based on outputs from the previously described wheel speed sensors 20 and 21 in step 100. Next, in step 110, a vehicle body speed VG is calculated based on the wheel speeds VW, etc. Here, either a maximum value or an average value of the wheel speeds VW can be used as the vehicle body speed VB.

In step 120, it is determined whether the brake switch 22 is on or off. At this time, the processing returns to step 100 to repeat the calculation of the wheel speeds VW and the like when the driver has not depressed the brake pedal 1 and the vehicle is not in the braking mode, that is, the brake switch 2 is off. In step 120, it goes to step 130 when the vehicle is in the braking mode and the brake switch 22 is on.

In step 130, based on the output from the stroke sensor 22, a pedal stroke PS, which is the amount of pedal input by the driver, is calculated. Next, in step 140, a pedal stroke change amount dPS, which is a change amount of input to the brake pedal 1, is calculated.

In step 150, it is determined whether a deceleration dVB of the vehicle body is larger than a predetermined value KV. The predetermined value KV may be set to a larger value to some extent, e.g., 0.4 G, that is, the deceleration value reached at the time when the driver suddenly brakes the vehicle. Here, if it is determined that the deceleration dVB of the vehicle body is smaller than the predetermined value KV, the processing returns to step 100. If it is determined that the deceleration dVB of the vehicle body is larger than the predetermined value KV, the processing goes to step 160.

In step 160, it is determined whether a pedal stroke PS is greater than a predetermined value KP. That is, it is determined whether the driver depresses the brake pedal 1 to provide a braking force greater than the predetermined value. The pedal stroke PS can be used, for example, to determine whether the driver merely requests the reduction of the vehicle speed requests or intends to stop the vehicle at a destination.

If it is determined in step 160 that the pedal stroke PS is smaller than a predetermined value KP, the processing returns to step 100. If it is determined that the pedal stroke PS is larger than the predetermined value KP, the processing goes to step 170. In step 170, it is determined whether a pedal stroke change amount dPS is within a predetermined range (Kdp1 < dPS < Kdp2). In other words, in the situation where the brake pedal 1 is depressed, it is determined whether the depression of the brake pedal 1 continues at an approximately constant value, continues to increase, or is released.

If it is determined in step 170 that the pedal stroke change amount dPS is outside the predetermined range, that is, a change in the stroke of the brake pedal 1 is determined, the processing returns to step 100. If it is determined that the stroke of the brake pedal 1 is substantially constant, the processing goes to step 180 to activate the booster device 100.

That is, in step 180, when the brake pedal 1 is depressed and the driver continues to depress the brake pedal 1, the brake fluid pressure applied to the first and second wheel cylinders 4 and 5 is increased by the increasing device 100 so that the braking force of the vehicle is increased. The deceleration of the vehicle increases accordingly.

The functions and effects of the flow chart described above are explained based on Fig. 3.

In Fig. 3, it is assumed that the deceleration dVB of the vehicle body has reached a value G1 which is larger than the predetermined value KV due to the driver's influence to gradually depress the brake pedal 1 in the period from time 0 to time t0. If it is also assumed that the depression of the brake pedal 1 is maintained and the pedal stroke hardly changes, the deceleration dVB of the vehicle body increases from a deceleration G1 to a deceleration G2 in the same period of time since the braking force is increased by the increasing device 100. Therefore, when there is a reaction force from the brake pedal 1, even under the condition that the driver maintains the depression of the pedal without further depression, the braking force is gradually increased by the increasing device 100 to cause an increase in the deceleration dVB of the vehicle body. In other words, due to the increase in the deceleration by the increasing braking force, even if the stroke of the brake pedal 1 is constant, a large braking force is ensured without requiring a strong depression of the brake pedal 1 by the driver.

Here, it is assumed that the driver continues to depress the brake pedal 1 in the period from t0 to time t1. Since the pedal stroke change amount dPS becomes larger than the predetermined value Kdp1, the increasing device 100 is not activated. However, an increase in the wheel cylinder pressure is carried out in accordance with the depression of the brake pedal 1, so that the braking force corresponding to the pedal depression is added.

It is also assumed that the driver releases the pedal depression a little in the period from t0 to time t2. The wheel cylinder pressure decreases according to this pedal influence, so that the braking force and also reduce the slowdown dVB of the vehicle body.

However, it is assumed that this release action of the depressed pedal from time t0 to time t2 is caused by an inappropriate action of the brake pedal 1 by the driver or a rebound action of the brake pedal 1 caused by the fact that the driver yields to the reaction force from the brake pedal 1 without any intention of reducing the braking force. It is also assumed that the driver again holds the pedal depression at time t2. As a result, the increasing device 100 increases the brake fluid pressure applied to the wheel cylinders 4 and 5 to increase the braking force when the pedal depression is held by the driver. The increase in the brake fluid pressure lasts as long as the state in which the deceleration dVB is greater than the predetermined value KV, the pedal stroke PS is greater than the predetermined value KP, and the brake pedal 1 is kept depressed at an approximately constant value. Therefore, even in a panic situation, as long as the deceleration dVB is greater than the predetermined value KV and the pedal stroke PS is greater than the predetermined value KP, the deceleration dVB is achieved by the increased braking force. That is, even if the depression of the brake pedal 1 is released to a certain extent and the depression of the brake pedal 1 is maintained at a certain value thereafter, a strong deceleration of the vehicle can be ensured.

Similarly, when the driver releases the depression of the brake pedal 1 in the period from time t2 to time t3, the deceleration dVB decreases while the brake pedal 1 is moving. However, if the depression of the brake pedal 1 is again at a certain value at time t3 is maintained, the braking force increases and a deceleration dVB is obtained. In this way, under the condition that the predetermined conditions are satisfied and repetition of depression and release of the brake pedal 1 is additionally carried out, a large braking force can always be obtained since the braking force is increased by the increasing device 100 at the time of holding the depression of the pedal.

When the pedal stroke PS becomes smaller than the predetermined value KP at time t4, this system determines that the panic braking is terminated or that the driver foresees that the vehicle will stop at the target point with certainty. Accordingly, the activation of the increasing device 100 is prohibited and the wheel cylinder pressure decreases normally by adjusting the wheel cylinder pressure according to the manipulation state of the brake pedal 1. When the depression of the brake pedal 1 is released, the system perfectly returns to a normal braking mode to set the wheel cylinder pressure and the braking force to zero.

As described above, according to the brake control device of the first embodiment, in the case where the pedal stroke is determined to be substantially constant, the braking force applied to the vehicle gradually increases by increasing the brake fluid pressure applied to the wheel cylinders at a predetermined increase ratio under the condition that both the deceleration and the pedal stroke are larger than the predetermined value. When the brake pedal 1 is released or further depressed, the braking force increases or decreases under the same condition according to the pedal manipulation. Therefore, once the driver depresses the brake pedal 1 sufficiently to obtain a large deceleration dVB of the vehicle body, simply holding the pedal depression a large braking force can be obtained. Even if the driver gradually releases the pedal depression, manipulating the holding of the pedal depression intermittently enables the driver to maintain the braking force at a high level. In addition, repetition of the release and depression of the brake pedal 1 enables the driver to obtain a substantially constant braking force. Therefore, the burden on the driver is reduced as compared with a conventional device which requires the driver to strongly depress the pedal.

The present invention is not limited to the first embodiment described above, but can be modified as described below.

For example, in the above-mentioned first embodiment, brake fluid is taken in by the pump 102 from the main reservoir 3a when the increasing device 100 shown in Fig. 1 is activated in step 180. However, it is not limited to this, as shown in Fig. 4, for example, the wheel cylinder pressures PW1 and PW2 can be increased by taking in brake fluid from the first pipe section A1 and discharging it to the second pipe section A2. In this case, the master cylinder pressure PU is also increased because the amount of brake fluid in the master cylinder 3 and the first pipe section A1 is reduced. Therefore, the driver can strongly depress the brake pedal 1 with a small load on his depression force without receiving a large pedal reaction force.

In the above-mentioned first embodiment, the two-way valve is used as the control valve 101 of the booster device 100. However, instead of the two-way valve, a structure can be used to control the pressure of the second line section A2 or the wheel cylinder pressure is maintained, both of which are increased by the increasing device 100 in step 180. More specifically, for example, a metering valve or a differential pressure regulating valve in which a relatively large differential pressure is set may be used. In other words, the retention of the pressure in the second line section A2 is achieved not only by preventing the flow of brake fluid from the side of the wheel cylinders 4 and 5 at the time of the master cylinder 3, but also by simply restricting the flow of the brake fluid from the side of the wheel cylinders 4 and 5 to the side of the master cylinder 3.

Furthermore, in the above-mentioned first embodiment, the booster 100 is activated in step 180 only when both the vehicle body deceleration dVB and the pedal stroke PS are greater than the predetermined values. However, the booster 100 may be set to be activated whenever the vehicle is in the braking mode.

Claims (14)

1. A braking control device for a vehicle, comprising: a brake operating element (1) that is operated by a driver to apply a braking force to the vehicle, the driver receiving the reaction force corresponding to an amount of operation of the brake operating element (1), a braking force generating device (2 to 5) for generating a braking force in the vehicle on the basis of the operating amount of the brake operating element (1), a determining device (50, step 170) for determining whether the operation amount is substantially unchanged and an increasing device (100) for increasing the braking force generated by the braking force generating device (2 to 5) as long as the amount of operation is substantially unchanged. 2. A brake control device for a vehicle according to claim 1, wherein the increasing means (100) continuously increases the braking force at a predetermined increasing ratio as long as the operation amount is kept substantially unchanged. 3. A brake control device for a vehicle according to claim 1, wherein the braking force generating device (2 to 5) comprises: a brake fluid pressure generating device (2 and 3) for generating a brake fluid pressure corresponding to the operating amount of the brake operating element (1), a wheel braking force generating device (4 and 5) for generating a braking force in a wheel when receiving the brake fluid pressure, and a line (A) for connecting the brake fluid pressure generating device (2 and 3) to the wheel braking force generating device (4 and 5), a line (A) for connecting the brake fluid pressure generating device (2 and 3) to the wheel braking force generating device (4 and 5). 4. A brake control device for a vehicle according to claim 3, wherein the determining means (50, step 170) determines whether the operation amount is substantially unchanged based on a change in the brake fluid pressure in the brake fluid pressure generating means (2 and 3). 5. A brake control device for a vehicle according to claim 3, wherein the brake actuating element (1) has a brake pedal, which is actuated by the driver, and the determining means (50, step 170) determines, based on a stroke amount of the brake pedal, whether a change in the operation amount is kept substantially unchanged. 6. A brake control device for a vehicle according to claim 3, wherein the wheel braking force generating device (4 and 5) causes a slowing down of the vehicle according to the brake fluid pressure, and the increasing means (100) continuously increases the deceleration of the vehicle by successively increasing the brake fluid pressure as long as the determining means (50, step 170) determines that the operation amount is kept substantially unchanged. 7. A brake control device for a vehicle according to claim 1, further comprising: a vehicle body deceleration detecting means (20 and 21, step 110) for detecting the deceleration of the vehicle body of the vehicle, wherein the increasing means (100) increases the braking force when the vehicle body deceleration detecting means (20 and 21, step 110) detects a vehicle body deceleration that is greater than a predetermined value. 8. A brake control device for a vehicle according to claim 1, wherein the increasing means (100) increases the braking force when the operation amount of the brake operating member (1) is greater than a predetermined value. 9. A brake control device for a vehicle according to claim 1, further comprising: a braking state detection device (22) for detecting whether the vehicle is in a braking state, wherein the increasing device (100) increases the braking force when the braking state detecting device (22) detects that the vehicle is in a braking state. 10. A brake control device for a vehicle according to claim 1, further comprising: a vehicle body deceleration detecting means (20 and 21, step 110) for detecting the vehicle body deceleration of the vehicle, and a prohibiting means (50, step 150) for preventing the increasing means from increasing the braking force, when the vehicle body deceleration detecting means (20 and 21, step 110) detects a vehicle body deceleration which is smaller than a predetermined value. 11. A brake control device for a vehicle according to claim 1, further comprising: a prevention device (50, stop 160) for preventing the increasing device (100) from increasing the braking force when the operating amount of the brake operating device (1) is less than a predetermined value. 12. A brake control device for a vehicle according to claim 1, further comprising: a braking state detecting means (22) for detecting whether the vehicle is in a braking state, and a preventing means (50, step 120) for preventing the increasing means (100) from increasing the braking force when the braking state detecting means (22) detects that the vehicle is not in the braking state. 13. A brake control device for a vehicle according to claim 1, wherein: the increasing device (100) stops increasing the braking force when the determining device (50, step 160) determines that the amount of operation changes substantially, and the braking force generating device (2 to 5) adjusts the braking force, which was increased by the increasing device (100), according to the actuation amount of the brake actuating element (1). 14. A brake control device for a vehicle according to claim 3, wherein the increasing device (100) comprises: a flow regulating element (101) located in the line (A) for regulating a flow of brake fluid from a side of the wheel braking force generating device (4 and 5) to a side of the brake fluid pressure generating device (2 and 3), and the increasing device (100) outputs pressurized brake fluid to the line (A) provided between the wheel braking force generating device (4 and 5) and the flow regulating element (101).